Ms Fishy Fishy is way larger than the other bettas I have.
I'm curious how big they have to be to be considered a giant.

Am in same boat, wish I had taken before / after pics. I believe one of the reasons my sorority has worked out so well is I introduced my gals (presently 6 in a 14 gallon) all roughly the same size and shopped around for the smallest ones so they can mature and grow up together.

Having said that, my red female has completely outgrown her gal pals. She wasn't the most aggressive at feeding time either during her growth spurt, so it wasn't like she was hogging all the food. To this day she is the most mellow female in my tank.